Routes to complexes of open chain polyethers

Abstract

The open chain polyethers, 1-(o-carboxymethoxyphenoxy)-2-(ohydroxyphenoxy) ethane HL(A), HL(B), and the diol were prepared and characterised by m.pt. and IR and 1H NMR spectroscopies.
In order to determine whether the ions other than Co(II) or Zn(ll) can form complexes of type [M(M'L2)2 (M = Transition element, M' = monovalent ion), the extraction of the metal ions Co(II), Ni(II), Cu(ll), Fe(ffl), Cr(ffl), and Pr(Ill) in the presence of K, Rb, Cs, and NH4 in an aqueous solution into the solutions of HL or HL(B) in methylene chloride was studied over a pH range.
In contrast to conclusions reached previous, it was found that the Cu(ll) was extracted as [CuL2] and not as [Cu(KL2)2]. The structure of the blue crystals grown from the organic solution was determined using DTG (1-120), AAS (Cu), UV, IX, EXAFS and microanalysis (C, H) and the crystal structure was determined by X-ray crystallography.
Attempts were made to substitute protonated amnes for the group 1 metals or NH4 ions in compounds of type [M(M'L2)2], (using HL and HL(B)) both in direct addition reactions and in solvent extraction studies. Extraction studies with some protonated amino esters, amino acids and alkyl ammOnium chlorides showed that Co(II), Ni(II), or Zn(ll) could not be extracted effectively from aqueous solution.
The work has shown that only a very few systems analogous to [Co(KL2)2] appear sufficiently stable for isolation and extraction studies; protonated organic amines seem relatively ineffectual. Accordingly, it was decided to explore the possibility of inserting phosphonate residues into polyether ligands to develop a new class of ligands. Although the presence of phosphorus containing crown ether systems is known, it was found that the direct insertion of the phosphonate residues on to polyether ligands is not possible.
As an another route to complexes of open chain polyethers, it was decided to introduce the open chain polyethers on to the phosphonateplatinum(II) complexes. Due to the requirement for a labile alkyl group on the phosphonate, it was decided to study the co-ordination chemistry of t-butyl phosphonate with platinum(ll).
In reactions between (RO)2PHO and [PtC12(COD)], (COD = cyclo-octa- 1,5-diene) greater steric hindrance when R = t-Bu inhibits formation of the normal product [Pt((RO)2POH)2{(RO)2P0)2] (R = Me, Et and Ph) and results in formation of the symmetrical chlorine bridged complex [Pt2C12RRO)2POH}2{(RO)2PO}2]. The bridge is readily cleaved by neutral
donors (L) to give cis-[PtC1(L){(RO)2POH}{(RO)2P0}] (L = amines, R3P, R3As, Ph3Sb, Ph3PSe, MeCN, DMSO), and trans-[PtC1(L){(RO)2POH}- ((RO)2P0)] where L = t-BuNC and Cl - to give [PtC12((RO)2POH)2]. In cis-[PtC1(L){(RO)2POH}{(RO)2P0}] the chloride ligand has been replaced by anionic ligands X, where X = Br, I, N3, NCO, NCS, NO2, 0NO2, 02CMe,
02CCF3, CN, CL!3, and H). The POH proton participates in an intramolecular hydrogen bond to the P0 group and may be replaced by Li or Na+.
The complexes provide a general route to complexes of primary phosphites (HO)2POR and of phosphorus(uI) acid; the t-butyl groups of cis- [PtC1(Ph3P) ((t-BuO)2POH) {(t-BuO)2P0}] are cleaved sequentially by CF3COOH, eventually forming cis-EPtC1(Ph3P){(H0)3P)RHO)2P0)], the crystal structure of which shows an approximately planar ring formed by Pt, two P0 groups and a connecting hydrogen bond. All complexes have been characterised by 31P NMR specroscopy.